The growth and carotenoid biosynthesis of the yeast Rhodotorula glutinis was studied by cocultivation with Lactobacillus helveticus in cheese ultrafiltrate containing 3.9% and 7.1% lactose. By growing this mixed culture in a 15-L fermentor MBR AG (Switzerland) at an air flow rate of 0.5 L/L min and agitation at 220 rpm for 6 days, a total yield of carotenoids of 268 mug/g dry cells wasobtained. Carotenoids were formed almost parallel with the cell growth, anda maximum production was reached at an early stationary phase. A high-performance liquid chromatographic system (HPLC) permitting simultaneous determination of major carotenoid pigments was used. The three main pigments (torularhodin, beta-carotene, and torulene) were formed in Rhodotorula glutinis, and reached a maximum concentration as follows: 182.0, 43.9, 23.0 mug,g dry cells. (c) 1994 John Wiley & Sons, Inc.

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An exopolysaccharide-producing Antarctic yeast strain was selected and identified as Cryptococcus laurentii AL₁₀₀. The physiological properties of the strain and its ability to utilize and biotransform different carbon sources (pentoses, hexoses, and oligosaccharides) into exopolysaccharide and biomass were investigated. Sucrose was chosen as a suitable and accessible carbon source. The biosynthetic capacity of the strain was studied in its dynamics at different sucrose concentrations (20, 30, 40, and 50 g/L) and temperatures (22 and 24 °C). The maximum biopolymer quantity of 6.4 g/L was obtained at 40 g/L of sucrose, 22 °C temperature and 96-h fermentation duration. The newly synthesized microbial carbohydrate was a heteropolysaccharide having the following monosaccharide composition: arabinose, 61.1%; mannose, 15.0%; glucose, 12.0%; galactose, 5.9%; and rhamnose, 2.8%. It was characterized by polydispersity of the polymer molecule, 60% of it having molecular mass of 4200 Da. The exopolysaccharide demonstrated good emulsifying and stabilizing properties with regard to oil/water emulsions and a pronounced synergistic effect with other hydrocolloids such as xanthan gum, guar gum, and alginate.

Psychrophilic Antarctic yeasts produce polysaccharides in different concentrations. According to morphological, cultural, physiological and biochemical characteristics, the best producer strain was identified as Cryptococcus flavus A(51). The highest values for viscosity (59.1 mPa s) and crude polysaccharide productivity (5.75 g/L) were obtained in a medium containing 5 % sucrose and 0.25 % (NH(4))(2)SO(4), at 24 degrees C for 6 d. The chemical composition and sugar constituents of the crude exopolysaccharide were determined (92.5 % saccharides, 3.34 % protein, and 4.16 % ash). The monosaccharide composition of the exopolysaccharide obtained from C. flavus strain AL(51) was established (55.1 % mannose, 26.1 % glucose, 9.60 % xylose, 1.90 % galactose). The microbial biopolymer has a high molar mass and homogeneity: 82 % of it had M 1.01 MDa.

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The effects of various carbon and nitrogen sources on the synthesis of exopolysaccharides by Rhodotorula acheniorum MC were studied. The dynamic viscosity of cell-free culture broths during exopolysaccharide synthesis were measured. The highest values for the viscosity (10.14 MPa.s) and crude polysaccharide productivity (6.6 g/L) were obtained in a medium supplied with 5% sucrose. Ammonium sulfate was the most favorable nitrogen source for exopolysaccharide synthesis. The value of pH played a determinant role, and the obligatory condition for exopolysaccharide production was low (pH 1.7-2.0) during the fermentation. The chemical composition and sugar constituents of the crude exopolysaccharides were determined. Mannose was the main monosaccharide component, and its concentration was the highest (69.13%) in the crude exopolysaccharide synthesized in the medium that included 5% sucrose as a carbon source.

Subject of study was the colloid chemical properties of the biopolymers mannan, synthesized from strain Rhodotorula acheniorum MC, and glucomannan, synthesized from strain Sporobolomyces salmonicolor AL(1). Their emulsifying capacity was studied in model systems of aqueous solutions in concentrations from 0.5% to 2.5% with regard to the aqueous phase. Emulsions of the direct type (oil/water) with 50% oil content were obtained. A disperse system with 2.5% glucomannan had 100% intact emulsion in the centrifugation test, while for the system with mannan, this indicator was 72%. Lab cream emulsions were obtained with glucomannan and with the emulsifiers Rofetan N/NS and Arlacel 165 used in the cosmetics industry. It has been established that under standard testing conditions, cream-like emulsions with 2.0% glucomannan have stability indicators comparable to these of 5.0% rofetan N/NS and 5.0% Arlacel 165. The samples with different concentrations of glucomannan showed a pseudo-plastic behaviour, as the highest viscosity was shown by the emulsion with 2.0% stored at 45 degrees C. The newly synthesized exopolysaccharides had a distinct emulsifying power and can be applied in the cosmetic and food industries.

The exopolysaccharide (EPS) production by psychrophilic Antarctic yeast Sporobolomyces salmonicolor AL₁ reached the maximum yield in medium containing sucrose (50 g/L) and diammonium sulfate (2.5 g/L) after a 5-d fermentation (5.64 g/L) at 22 °C, the dynamic viscosity of the culture broth reaching (after 5 d) 15.4 mPa s. EPS showed a mannan-like structure and high molar mass, and did not affect cellular viability and proliferation of murine macrophages. It exhibited also a protective effect against the toxic activity of Avarol.